Metal droplet jetting system

ABSTRACT

Systems and methods for additive manufacturing, and, in particular, such methods and apparatus as employ pulsed lasers or other heating arrangements to create metal droplets from donor metal micro wires, which droplets, when solidified in the aggregate, form 3D structures. A supply of metal micro wire is arranged so as to be fed towards a nozzle area by a piezo translator. Near the nozzle, an end portion of the metal micro wire is heated (e.g., by a laser pulse or an electric heater element), thereby causing the end portion of the metal micro wire near the nozzle area to form a droplet of metal. A receiving substrate is positioned to receive the droplet of metal jetted from the nozzle area.

RELATED APPLICATIONS

This is a CONTINUATION of U.S. application Ser. No. 16/185,458, filed 9Nov. 2018, which is a NONPROVISIONAL of and claims priority to, U.S.Provisional Application No. 62/586,311, filed 15 Nov. 2017, each ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to methods and apparatus foradditive manufacturing, and, in particular, to such methods andapparatus as employ pulsed lasers or other heating arrangements tocreate metal droplets from donor micro wires, which droplets, whensolidified in the aggregate, form three-dimensional (“3D”) structures.

BACKGROUND

So-called “3D printing” or, more generally, additive manufacturing, is abroad term used to describe processes to fabricate three-dimensionalobjects from digital data files under computer control. A number ofdifferent additive manufacturing techniques have been developed, some ofwhich involve the fusing of material, typically a metal, polymer, orceramic powder, using a laser. A more recent additive manufacturingprocess known as laser-induced forward transfer (“LIFT”), illustrated inFIG. 1, creates and ejects metal droplets from a thin metal foil or filmdisposed on a back side (from the standpoint of the incident laser beam)of transparent substrate. To form the droplets, a laser is focused on asmall area of the metal foil through the transparent substrate on whichit is carried. Local heating caused by the laser causes a droplet of themetal foil to be jetted, where the size of the droplet is proportionalto the cross-section of the laser beam incident on the foil. The dropletso ejected travels across a gap (typically on the order of a fewmicrons) and coalesces on a recipient substrate. See, e.g., Zenou, M. etal., “Laser jetting of femto-liter metal droplets for high resolution 3Dprinted structures,” Scientific Reports 5, 17265; doi: 10.1038 (2015).This technique is applied to printing of 3D structures by jettingoverlapped metal droplets in shapes defined by cross-sections of theobject being printed.

SUMMARY OF THE INVENTION

Described herein are systems and methods for additive manufacturing,and, in particular, such methods and apparatus as employ pulsed lasersor other heating arrangements to create metal droplets from donor microwires, which droplets, when solidified in the aggregate, form 3Dstructures.

In one embodiment, a system for metal laser jetting includes a supply ofmetal micro wire (e.g., having a diameter of approximately 10 microns)arranged so as to be fed towards a nozzle area by a piezo translatorand/or motorized translator. The metal micro wire is supported along itslength in a through hole of a glass substrate (e.g., fused quartz, fusedsilica, or ceramic glass), and the nozzle area is located at an exit ofthe through hole. A laser is positioned to emit, under the control of acontroller, a light pulse (e.g., IR, UV, or visible light, with theglass substrate being transparent, or nearly so, at a wavelength of thelaser light pulse) towards the nozzle area where the end of the metalmicro wire is positioned by the piezo translator, thereby causing an endportion of the metal micro wire near the nozzle area to be heated. Areceiving substrate is positioned to receive a droplet of metal jettedfrom the nozzle area. A heater may be affixed to one or more sides ofthe glass substrate to preheat the metal micro wire.

Preferably, the supply of metal micro wire is organized in a spool whichis carried on a reel. In some instances, the supply of metal micro wireis organized in multiple spools of metal micro wires, each associatedwith its own respective piezo translator (and/or motorized translator)and supporting glass substrate arrangement. Alternatively, the supply ofmetal micro wire may be organized in multiple spools of metal microwires and a single glass substrate shared by some or all of the spoolsof metal micro wires. In any or all of these instances, the supply ofmetal micro wire may be arranged so as to be fed towards the nozzle areaby the piezo translator via one or more rollers.

The piezo translator may include one or more piezo ceramics arranged tomove the metal micro wire in a defined direction upon application of anelectric current under the control of the controller. In some cases, thepiezo translator may include one or more longitudinal piezo actuators,one or more piezoelectric shear actuators, or one or more tubeactuators. Additional piezo translators may be arranged to rotate a reelon which a spool of the metal micro wire is carried about a centralaxis, thereby playing out the metal micro wire towards the nozzle area,under the control of the controller.

In some embodiments, the laser is included in a scanning laserarrangement configured to scan, under the control of the controller, asingle laser beam over a scanning path so that the laser beam, whenactivated, is incident upon one of a plurality of nozzle areasassociated with a respective one of the metal micro wires. Such ascanning laser arrangement may include a scanning mirror or anacousto-optic deflector.

As described further below, the glass substrate may be associated with aform shaped to change an orientation of the metal micro wire from afirst plane to a second plane as the metal micro wire is fed towards thenozzle area. Also, the glass substrate may define a reaction area inwhich the metal micro wire is exposed to the light pulse. For example,the nozzle area may make up a portion of such a reaction area and asecond piezo translator may be positioned adjacent the nozzle area. Sucha reaction area may include a gas inlet to allow for the introduction ofa pressurized gas.

In further embodiments of the invention, a 3D article is manufactured byfusion of metal droplets in forms defined by cross-sections of thearticle under construction. Such a method may include distributingsuccessive layers of metal droplets over a receiving medium andpreviously deposited layers of metal droplets by depositing the dropletswhile moving the receiving medium relative to a nozzle area of a metallaser jetting system in which a supply of metal micro wire is fedtowards the nozzle area at which an end portion of the metal micro wireis heated by a laser pulse emitted from a laser under the control of acontroller and incident towards the nozzle area, thereby causing the endportion of the metal micro wire near the nozzle area to form thedroplets. Moving the receiving medium relative to the nozzle areabetween successive ones of the droplets thus forms layers of metal onthe receiving medium and, successively, on previously jetted layers.

In such a method, the controller may cause the laser to emit pulses,thereby creating the metal droplets, at times corresponding to necessaryapplications of metal for forming the cross-sections of the articleunder construction according to provided images of the cross-sectionsand ensuring that the metal droplets are jetted when a portion of thereceiving medium is positioned below the nozzle area at a point forwhich solid material is needed. Also, after each droplet is jetted, thecontroller may cause a piezo translator (and/or motorized translator) toadvance a quantity of the metal micro wire into the nozzle area inpreparation for a next laser pulse. At or about the same time as causingthe piezo translator to advance the quantity of the metal micro wireinto the nozzle area, the controller may further cause the receivingmedium to be displaced relative to the nozzle area to a next position atwhich a metal droplet is to be jetted.

In some embodiments, the article under construction is imaged during itsconstruction using an imaging device. Images of the deposited layers ofmetal droplets may thus be analyzed as they are being formed, and thelaser pulses incident on the metal micro wire controlled in accordancesuch an evaluation. Alternatively, or in addition, such imaging of thearticle under construction during its construction may be used as abasis for modifying an image of a cross-sectional layer of the articleunder construction so that one or more areas of the image are adjustedfrom those associated with an original version of said image.

As indicated above, the supply of metal micro wire may be organized inmultiple spools of metal micro wires and, accordingly, the laser may bescanned (e.g., using a mirror, an acousto-optic deflector, etc.) over ascanning path so that the laser pulse, when activated, is incident uponone of a plurality of nozzle areas associated with a respective one ofthe metal micro wires.

Still further embodiments of the invention provide a system for metallaser jetting that includes a supply of metal micro wire arranged so asto be fed towards a reaction area having an associated nozzle area by apiezo translator, the metal micro wire being supported along its lengthin a through hole of a form, the nozzle area being located near an exitof the through hole; and a heater positioned to contact an end of themetal micro wire adjacent the nozzle area, thereby causing an endportion of the metal micro wire near the nozzle area to be heated. Insuch systems, the form may be shaped to change an orientation of themetal micro wire from a first plane to a second plane as the metal microwire is fed towards the nozzle area. In some embodiments of such asystem, a second piezo translator (and/or motorized translator) may bepositioned adjacent the nozzle area, and the heater being positioned soas to be displaceable towards the end of the metal micro wire by thesecond piezo translator.

Still further embodiments of the invention provide a method of forming a3D article by fusion of metal droplets is which successive layers ofmetal droplets are deposited over a receiving medium (and previouslydeposited layers of metal droplets) by depositing the droplets whilemoving the receiving medium relative to a nozzle area of a metal laserjetting system in which system a supply of metal micro wire is fedtowards the nozzle area at which an end portion of the metal micro wireis heated by a heater, thereby causing the end portion of the metalmicro wire near the nozzle area to form the droplets, said movingoccurring between successive ones of the droplets to form layers ofmetal on the receiving medium and, successively, on previously jettedlayers. As the metal micro wire is fed towards the nozzle area the metalmicro wire may pass through a through hole in a form. The reaction areais disposed within the form such that a portion of the metal micro wireis exposed within the reaction area when exiting the through hole. Priorto heating of the metal micro wire, the reaction area may be filled witha gas introduced through a gas inlet.

The heater may be operated under control of a controller and affixed toan end of a piezo translator. The piezo translator may thus be operatedso as to cause the heater to abut an exposed end of the micro metal wirenear the nozzle area, thereby heating the end of the metal micro wirenear the nozzle area and forming a metal droplet.

These and further embodiments of the invention are discussed in greaterdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings, in which:

FIG. 1 illustrates aspects of the LIFT additive manufacturing process.

FIG. 2 illustrates one example of a system for metal laser jetting inaccordance with one embodiment of the invention.

FIG. 3 illustrates another example of a system configured in accordancewith various embodiments of the invention, which include multiple spoolsof metal micro wires, each associated with its own piezo translator andsupporting glass substrate arrangement.

FIG. 4 shows a further example of a system in accordance with variousembodiments of the invention in which multiple spools of metal microwires share a single, common piezo translator.

FIG. 5 illustrates yet another embodiment of the present invention thatincludes multiple metal micro wires and a scanning laser arrangement.

FIG. 6 shows an arrangement similar to that illustrated in FIG. 5,however, in this instance the scanning laser arrangement has beenreplaced by a laser beam distributor which distributes the laser beam toindividual fiber optic transmission lines, one each associated with anindividual nozzle area.

FIG. 7 shows a close up of a nozzle area and one example of a scanningor focusing arrangement for embodiments of the present invention.

FIGS. 8A-8H illustrate steps in a process for metal droplet jetting inaccordance with some embodiments of the present invention.

FIG. 9 illustrates yet another embodiment of the present invention inwhich a portion of a reaction area above a metal wire is filled with aglass substrate.

FIG. 10 illustrates an embodiment of the present invention in which aportion of a reaction area above a metal wire is filled with ahigh-pressure gas, introduced through a gas inlet.

FIG. 11 is a top view of a system that includes opposing pairs ofmultiple spools of metal micro wires, some or all of which may be ofdifferent kinds of metals, arranged in systems similar to thatillustrated in FIGS. 9 and 10 and sharing a common form.

FIGS. 12A and 12B show variants of the systems depicted in FIGS. 9 and10 but replace a laser with an electric heater positioned on an end of apiezo translator.

FIGS. 13A-13F illustrate the formation of a metal droplet in systemssimilar to that shown in FIG. 12A.

FIG. 14 illustrates a further example of a system embodying the presentinvention in which a metal micro wire is disposed within an arrangementconfigured to cause jetting of metal droplets.

DESCRIPTION

The present invention concerns an additive manufacturing technique inwhich one or more pulsed lasers or other heating arrangements createmetal droplets from donor micro wires, which droplets, when solidifiedin the aggregate, form 3D structures on a receiving substrate. In theLIFT technique discussed above, a metal is thermally evaporated orsputtered onto a plastic foil to provide a metal layer of approximately1 μm thickness. The use of donor micro wires as in the presentinvention, and not metalized foils (e.g., thin metal layers deposited ona transparent substrate), offers improvements over the LIFT techniquediscussed above. For example, by using metal micro wires, less waste isproduced inasmuch as the micro wire can be formed into droplets seriallyalong its length, as needed, without wasting material as may be the casewith metal foils. Further, metal micro wires may be fashioned relativelyeasily and inexpensively through conventional extrusion processes. Thismay assist in reducing the overall cost of systems for metal laserjetting.

Referring now to FIG. 2, a first example of a system 10 for metal laserjetting in accordance with one embodiment of the invention isillustrated. In this example, a metal micro wire is organized in a spool14 which is carried on a reel 16, and is fed towards a nozzle area 18 bya piezo translator (and/or motorized translator) 20 via one or morerollers 22. The metal micro wire 12 is supported along its length in athrough hole 34 (which may have a tapered entrance) of a transparent,high temperature resistant (or tolerant) glass substrate 24 to ensurethe wire does no bend or break. Examples of materials which may be usedfor glass substrate 26 include fused quartz, fused silica, and ceramicglass. The nozzle area 18 is located at the exit of through hole 34. Aheater 26 may be affixed to one or more sides of the glass substrate 24to preheat the metal micro wire, though in other embodiments the heatermay be omitted. A laser 28 emits, under the control of a controller 30,a pulse, preferably in the IR wavelengths, e.g., at or about 1 μm-10 μm,(but which could be in UV or visible wavelengths) towards the nozzlearea 18, where the end of the metal micro wire is positioned by piezotranslator 20. The glass substrate 24 is transparent (or nearly so) atthe wavelength of the laser light, so that the energy imparted by thelaser light is primarily absorbed by the metal micro wire, causing theend portion of the metal micro wire, which has a diameter on the orderof 10 microns, near the nozzle area to be heated very rapidly. Localheating of the metal micro wire caused by the laser beam causes adroplet of metal to be jetted from the nozzle area 18. Although notshown in FIG. 1, the nozzle area 18 may be in close proximity to areceiving substrate on which the droplet 32 is deposited. Jettingoverlapped metal droplets in this fashion in shapes defined bycross-sections of the object being manufactured results in the formationof the object.

Although not shown in detail in FIG. 1, the piezo translator 20 includesa piezo ceramic that expands in a defined direction upon application ofan electric current (e.g., under the control of controller 30). Theceramic is orientated to abut the micro wire 12 so that when the ceramicexpands (at the application of a current under the control of controller30), the micro wire is moved along a single axis (e.g., parallel to itslongest dimension), along the direction of the expansion of the crystal,e.g., by friction. Generally, a number of piezo translators will be usedto move the micro wire and the various piezo translators may beenergized at the same time (or nearly so) so that their actions arecoordinated with one another. Thus, the piezo translators are arrangedso that they impart longitudinal motion to the micro wire in the samedirection and the translation distance may be proportional to themagnitude of the current applied to the piezo translators. In someembodiments, the translation distance of the micro wire for eachactivation of the piezo translators is on the order of a tens ofnanometers to a few microns. Preferably, the reel 16 on which the spool14 of micro wire is maintained is mounted on an axial pin or otherelement (not shown) with frictionless, or nearly so, bearings so as toprovide minimal resistance when the micro wire is translated by thepiezo translators.

The piezo translator(s) employed in embodiments of the present inventionmay be any of: longitudinal piezo actuator, in which an electric fieldin the ceramic is applied parallel to the direction of its polarization:piezoelectric shear actuators, in which the electric field in theceramic is applied orthogonally to the direction of its polarization; ortube actuators, which are radially polarized and have electrodes areapplied to an outer surfaces of the ceramic so that the field parallelto its polarization also runs in a radial direction. In otherembodiments, one or more piezo translators may be arranged to rotate thereel 16 on which the spool 14 of metal micro wire is carried about itscentral axis, playing out the metal micro wire 12 towards the nozzlearea 18. Such an arrangement may be well suited for instances where thedistance between the point at which the metal micro wire is taken offthe spool 14 and the nozzle area 18 is relatively short and/or where themetal micro wire is supported along the majority of its length so thatit does not bend between these points. Such an arrangement may be usedin combination with the linear translator 20 described above, with themultiple piezo translators arranged to actuate at the same time underthe control of controller 30.

In one embodiment, controller 30 includes a processor that executescomputer-readable instructions (i.e., computer programs or routines)defining methods as described herein, which methods are instantiated andrun on non-transitory computer-readable media. Such processes may berendered in any computer language and executed on any suitableprogrammable logic hardware. Processor-based controllers 30 upon or withwhich the methods of the present invention may be practiced willtypically include a bus or other communication mechanism forcommunicating information; a main memory, such as a RAM or other dynamicstorage device, coupled to the bus for storing information andinstructions to be executed by the processor and for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by the processor; and a ROM or other staticstorage device coupled to the bus for storing static information andinstructions for the processor. A storage device, such as a hard disk orsolid-state drive, may also be included and coupled to the bus forstoring information and instructions. The subject controller may, insome instances, include a display coupled to the bus for displayinginformation to a user. In such instances, an input device, includingalphanumeric and/or other keys, may also coupled to the bus forcommunicating information and command selections to the processor. Othertypes of user input devices, such as cursor control devices may also beincluded and coupled to the bus for communicating direction informationand command selections to the processor and for controlling cursormovement on the display.

The controller 30 may also include a communication interface coupled tothe processor, which provides for two-way, wired and/or wireless datacommunication to/from the controller, for example, via a local areanetwork (LAN). The communication interface sends and receiveselectrical, electromagnetic, or optical signals which carry digital datastreams representing various types of information. For example, thecontroller 30 may be networked with a remote unit (not shown) to providedata communication to a host computer or other equipment operated by auser. The controller can thus exchange messages and data with the remoteunit, including diagnostic information to assist in troubleshootingerrors, if needed.

In operation, system 10 may be used for forming a 3D article by fusionof metal droplets 32 in forms defined by cross-sections of the objectunder construction. For example, a first layer of individual dropletsmay be distributed over a receiving medium (not shown). This may beaccomplished by depositing the droplets while moving the receivingmedium with respect to the nozzle area between successive droplets toform the relatively thin, approximately uniform layers of metal on thereceiving medium and, successively, on previously jetted layers. Oncejetted, the droplets cool and solidify in place.

Controller 30 is programmed to cause the laser 28 to emit pulses,thereby creating droplets 32, at times corresponding to the necessaryapplication of metal for forming the cross-section of the article underfabrication. This may be done, for example, by providing images ofcross-sections, and ensuring that the metal droplets are jetted when aportion of the receiving medium is positioned below the nozzle area 18at a point for which solid material is needed. After each droplet isjetted, controller 30 causes piezo translator 20 to advance a quantityof metal wire 12 into the now vacant nozzle area, in preparation for thenext application of the laser pulse. At or about the same time, thecontroller 30 may cause the receiving medium to be displaced relative tothe nozzle area 18 to a next position at which a metal droplet is to bejetted. The fusion of metal droplets in locations on the receivingmedium corresponding to the image of the cross-sectional layer of theobject to be fabricated form an integral layer of metal having a shapecorresponding to that image. In addition, supporting structures may befabricated during production of the object and later removed. Successivelayers of metal droplets are jetted on top of one another to completethe object.

During the fabrication process, images of the object under fabricationmay be taken (successively or continuously) e.g., using infra-redimaging devices and/or charge coupled device (CCD) cameras. Byevaluating images of the metal layers as they are being formed, thelaser light incident on the metal wire may be controlled in accordancetherewith. For example, an image of a cross-sectional layer of the 3Darticle used to produce the article under fabrication may be modifiedaccording to feedback provided by one or more imaging devices so thatone or more areas of the image are adjusted from those associated withan original version of image. Such feedback may be used to compensatefor inadequate metal deposition in one or more areas and/or variationsin metal droplet displacement prior to cooling sufficiently to fuse witha portion of an existing structure.

FIG. 3 illustrates an example of a system 10′ configured in accordancewith some embodiments of the invention, and which includes multiplespools 14 a-14 n of metal micro wires, each associated with its ownpiezo translator (and/or motorized translator) 20 a-20 n and supportingglass substrate arrangement 24 a-24 n. In some instances, a single glasssubstrate 24 shared by some or all of metal wire spools 14 may be used.Although the figure shows only 3 wire spools, each on different reels,and each potentially a different material, disposed in separate,adjacent jetting arrangements, for ejecting droplets of different kindsof metals, it should be appreciated that systems with any number ofreels and kinds of metal wires may be used. Further, although not shownin detail, one should recognize that systems such as 10′ may beconfigured with one or more lasers, for example dedicated lasers foreach metal wire spool or fewer lasers shared between various ones of themetal wire spools. Also, components of system 10 may be under the commoncontrol of a single controller such as that shown in FIG. 2, or multiplesuch controllers, configured to act in concert with one another eitherthrough appropriate programming, networked communications (with oneanother and/or a remote unit), or both. Systems such as 10′ are usefulfor jetting arrangements in which different materials are used, and/orwhere the presence of multiple where spools speeds fabrication of asingle object.

FIG. 4 shows a further example of a system 10″ in which multiple spools14 a-14 n of metal micro wires share a single, common piezo translator20′. Other components of this arrangement are as discussed above withrespect to FIGS. 2 and 3.

FIG. 5 illustrates one embodiment of the present invention that includesmultiple metal micro wires 12 a-12 n, and a scanning laser arrangement40. In this example, multiple metal micro wires 12 a-12 n are guided viaa common supporting glass substrate arrangement 24, and a scanning laserarrangement 40 is used to scan (under the control of a controller 30) asingle laser beam 44 over a scanning path 46 so that the beam (whenactivated) is incident upon one of the desired nozzle areas 18 a-18 nassociated with a respective one of the micro wires 12 a-12 n. Scanningof the laser beam may be effected using a scanning mirror or otherarrangement (e.g., an acousto-optic deflector). The laser may be pulsed,as discussed above, so that it is not in continuous operation duringscanning of the beam. By using a scanning arrangement of this kind, asingle laser may be employed with multiple spools of metal micro wire.

FIG. 6 shows an arrangement similar to that illustrated in FIG. 5,however, in this instance the scanning laser arrangement has beenreplaced by a laser beam distributor 50 which distributes the laser beam44 to individual fiber optic transmission lines 52, one each associatedwith nozzle areas 18 a-18 n. The fiber optic distributor may includearrangements of mirrors, lenses, beam splitters, diaphragms, etc., thatoperate under the control of controller 30 so as to provide laser pulsesto selected ones of nozzle areas 18 a-18 n for the creation of metaldroplets. Near each nozzle area, the fiber optic transmission linesterminate at or near focusing elements (e.g., lens arrangements) thatfocus 54 the emitted laser light onto the respective metal micro wiresat the respective nozzle areas. This is another way in which a singlelaser may be employed with multiple spools of metal micro wire.

FIG. 7 shows a close up of a nozzle area 18 and one example of ascanning or focusing arrangement for embodiments of the presentinvention. In this example, a laser beam 44 is focused by a one or morefocusing elements 56 (e.g., lenses) to be incident upon a mirror 58,which redirects the beam on the metal wire 12 so that its point of focusis at or near the nozzle area 18. In some cases, the mirror may be ascanning mirror which also scans the beam 44 across multiple metal wires(not shown in this figure). Alternatively, where focusing elements 56are not used, the mirror 58 may be a focusing mirror (e.g., a mirrorhaving a concave parabolic curvature) that focuses the beam 44 onto themetal wire 12 near nozzle area 18.

FIGS. 8A-8H illustrate steps in a process for metal droplet jetting inaccordance with some embodiments of the present invention. In FIG. 8A,the metal micro wire 12 is in position within the through hole of glasssubstrate 24, with the end of the micro wire disposed at or near thenozzle area 18. The temperature of the glass substrate, T_(s), is at ornear the ambient temperature of the environment T_(ambient), and thetemperature of the micro wire, T_(w), is at or near that of the glasssubstrate, T_(s). No laser pulse has yet been applied to the wire andheating element 26 is not applying any heat to the glass substrate.

In FIG. 8B, heater 26 has been activated and is heating the glasssubstrate 26 so that T_(s)<<T_(ambient). Preferably, the glass substrate26 is made of a material having very good thermal conductivity and a lowcoefficient of thermal expansion, e.g., fused silica, fused quartz, orceramic glass, and so heat is conducted through the glass substrate toheat metal micro wire 12 so that T_(w)˜>T_(s). No laser pulse has yetbeen applied to the wire.

In FIG. 8C, when T_(w) has reached a desired temperature, or afterapplication of heat from heater 26 for a desired time, laser pulse 44 isapplied (under the control of the controller, not shown) to the metalmicro wire at a location near the nozzle area 18. The application of thelaser pulse causes the metal micro wire to be heated to temperaturesnear or at its melting point, but only in a localized area near thepoint at which the laser pulse is applied (the time of the processillustrated in FIGS. 8C-8D will determine the size of the localizedarea). As shown in FIG. 8D, as the laser pulse continues to be applied,the area of local heating of the metal micro wire increases so that thewire is heated throughout its cross-section over a small longitudinalextent. To assist in creating this area of local heating, the laser beam44 may be scanned, e.g., under the control of the controller using asmall mirror, moveable lens, or other scanning arrangement, over a smallextent of the micro wire as it is positioned in the through hole of theglass substrate 24 near the nozzle area 18. Scanning the laser beam inthis fashion may provide for creation of a metal droplet in a moreuniform fashion than if one is allowed to form from application of astationary beam. Alternatively, a single laser beam could be decomposedinto multiple beams and/or shaped to an ellipsoid or other cross-section(e.g., by lenses), to cover a greater extent of the metal micro wire.

In FIG. 8E, in order to promote expulsion of the metal droplet, theenergy of the laser pulse may be briefly increased, as shown in FIG. 8F,causing the molten metal to vaporize, thereby disassociating andexpelling the droplet 32 from the rest of the metal micro wire 12through nozzle 18. Upon formation of the metal droplet 32, the laserpulse is discontinued. This may be based on visual feedback provided bya camera monitoring system, or based on time of application of thepulse, or both. For example, the controller may be programmed todiscontinue the laser pulse after a time, T_(pulse), since it wasinitiated, unless visual feedback indicates that a droplet 32 is earlierformed, at which point the controller may discontinue application of thelaser pulse.

As shown in FIG. 8G, after a droplet has been formed and expelled, thelaser beam 44 is again applied to the end of the metal micro wire, whichis now displaced some distance above the nozzle area 18 at the end ofthe through hole in the glass substrate. The change in focal point ofthe laser beam may be made under the control of the controller bydisplacing the beam through an arc of known magnitude using mirrors,movable lenses, or other scanning arrangement. The application of thelaser to the end point of the metal wire is timed to take place at orabout the same time as the piezo translator (not shown in thisillustration) is active to translate the wire towards the nozzle area18. Heating the wire in this fashion assists in the translationoperation by ensuring that the end of the wire, which has now cooledsomewhat from temperatures reached during previous application of thelaser pulse, do not adhere to the sidewalls of the through hole, therebyimpeding movement of the wire within the through hole of the glasssubstrate. The piezo translator is operated, under control of thecontroller, to move the wire a distance sufficient to bring the end ofthe wire close to the nozzle area 18, as shown in FIG. 8H, so that theforegoing process may be repeated for the next metal droplet. This mayagain be a timed operation, or one conducted using visual feedback froma camera monitoring system, or both.

FIGS. 9 and 10 illustrate, respectively, systems 70 and 70′, which arealternative arrangement for a metal jetting system configured inaccordance with further embodiments of the present invention. In theseexamples, the metal micro wire is organized in a spool 14 which iscarried on a reel 16, and is fed towards a nozzle area 18 by a piezotranslator 20 via one or more rollers 22. Along the way, the metal wire12 passes through a form 74, made of a high temperature resistantmaterial, e.g., one with a very low coefficient of thermal expansion.The metal micro wire 12 is supported along its length in a through hole76 (which may have a tapered entrance) of the high temperature resistantform 74, which may be articulated to change the orientation of the wirefrom a first, vertical plane, to a second, horizontal plane. Examples ofmaterials which may be used for form 74 include fused quartz, fusedsilica, and ceramic glass.

Within the form 74 is a reaction area 78. Reaction area 78 may becylindrical or rectangular in cross section, and extends through form74, exposing wire 12 on both sides such that when wire 12 is threadedthrough the through hole 76 it exits the form within the reaction area78. In system 70, shown in FIG. 9, the portion of the reaction area 78above the metal wire 12 is filled with a glass substrate 24 havingproperties similar to those described above. Below the metal wire 12,the reaction area 78 is tapered or of a reduced diameter, so that nozzlearea 18 is formed. In this example, a portion of the reaction areasidewall is removed, and replaced with a piezo translator 72. In system70′ shown in FIG. 10, the portion of the reaction area 78 above themetal wire 12 is filled with a high-pressure gas, preferably an inertgas such as Argon or Helium, introduced through gas inlet 80. Below themetal wire 12, the reaction area 78 is tapered or of a reduced diameter,so that nozzle area 18 is formed. A portion of the reaction areasidewall is removed, and replaced with a piezo translator 72. In thisexample, rather than a heat resistant glass substrate, a thin,transparent (at the wavelength of the laser pulse) membrane 84 may beused as a cap for the reaction area 78. The transparent membrane may bemade of fused quartz, fused silica, or ceramic glass, or a lessexpensive material such as a tempered glass. The use of a gas withinreaction area 78 as in this example helps to minimize or preventoxidation of that portion of metal wire 12 exposed within the reactionarea 78.

With systems 70 and 70′, laser 28 emits, under the control of controller30, a pulse, preferably in the IR wavelengths, e.g., at or about 1 nm-10nm, towards the portion of metal wire 12 exposed above nozzle area 18,where the end of the metal micro wire has been positioned by piezotranslator 20. The energy imparted by the laser light is primarilyabsorbed by the metal micro wire, causing the end portion of the metalmicro wire, which has a diameter on the order of 10 microns, near thenozzle area to be heated very rapidly. Local heating of the metal microwire caused by the laser beam 44 causes a droplet of metal 32 to bejetted from the nozzle area 18. Although not shown in theseillustrations, the nozzle area 18 may be in close proximity to areceiving substrate on which the droplet 32 is deposited. Jettingoverlapped metal droplets in this fashion in shapes defined bycross-sections of the object being manufactured results in the formationof the object. Formation of a metal droplet in systems such as 70 and70′ is similar to that described above, with the laser 28 beingactivated for pulses to heat the wire in areas adjacent nozzle area 18,causing the wire to melt and form droplets which are jetted out. Asdiscussed in greater detail below, piezo transducer 72 may be actuated,under the control of controller 30, during formation of the droplet toassist in its ejection from the nozzle area 18 and/or adjusted tocontrol the amount of wire 12 exposed to the laser so as to control thesize of the droplet. In embodiments were a high-pressure gas 82 is used,the gas likewise assists in expelling the metal droplet 32 towards thereceiving material.

FIG. 11 is a top view of a system 70″, which includes opposing pairs ofmultiple spools 14 a-14 n of metal micro wires 12 a-12 n, some or all ofwhich may be of different kinds of metals, arranged in systems similarto that illustrated in FIGS. 9 and 10, and sharing a common form 76.Although this example is illustrated with a glass substrates 24, similarsystems may be used with membranes 84 and associated high pressure gassystems.

FIGS. 12A and 12B show variants of the systems depicted in FIGS. 9 and10, but replace the laser 28 with an electric heater 84 positioned onthe end of the piezo translator 72. In the example shown in FIG. 12A,the metal micro wire 12 is organized in a spool 14 which is carried on areel 16, and is fed towards a nozzle area 18 by a piezo translator 20via one or more rollers 22. Along the way, the metal wire 12 passesthrough a form 74, made of a high temperature resistant material, e.g.,one with a very low coefficient of thermal expansion. The metal microwire 12 is supported along its length in a through hole 76 (which mayhave a tapered entrance) of the high temperature resistant form 74,which may be articulated to change the orientation of the wire from afirst, vertical plane, to a second, horizontal plane. Examples ofmaterials which may be used for form 74 include fused quartz, fusedsilica, and ceramic glass.

Within the form 74 is a reaction area 78. Reaction area 78 may becylindrical or rectangular in cross section, and extends partiallywithin form 74, exposing wire 12 on both sides such that when wire 12 isthreaded through the through hole 76 it exits the form within thereaction area 78. In the system shown in FIG. 12A, the reaction area 78is filled with a high-pressure gas, preferably an inert gas such asArgon or Helium, introduced through gas inlet 80. The use of a gaswithin reaction area 78 as in this example helps to minimize or preventoxidation of that portion of metal wire 12 exposed within the reactionarea 78. Below the metal wire 12, the reaction area 78 is tapered or ofa reduced diameter, so that nozzle area 18 is formed. A portion of thereaction area sidewall is removed, and replaced with a piezo translator72.

An electrical heater 84, operated under the control of controller 30, isaffixed to the end of the piezo translator 72 and abuts the exposed endof micro metal wire 12 near the nozzle area 18, where the end of themetal micro wire has been positioned by piezo translator 20. The energyimparted by the electrical heater is used instead of a laser to melt theend of micro wire 12 near the nozzle area 18 and form a metal droplet.Although not shown in the illustration, the nozzle area 18 may be inclose proximity to a receiving substrate on which the metal droplet isdeposited. Jetting overlapped metal droplets in this fashion in shapesdefined by cross-sections of the object being manufactured results inthe formation of the object. Piezo transducer 72 may be actuated, underthe control of controller 30, during formation of the droplet to assistin its ejection from the nozzle area 18 and/or adjusted to control theamount of wire 12 exposed to the laser so as to control the size of thedroplet. In embodiments were a high-pressure gas 82 is used, the gaslikewise assists in expelling the metal droplet 32 towards the receivingmaterial.

FIG. 12B shows an alternative arrangement of a system similar to thatillustrated in FIG. 12A. In the example shown in FIG. 12B, the metalmicro wire 12 is organized in a spool 14 which is carried on a reel 16,and is fed towards a nozzle area 18 by a piezo translator 20 via one ormore rollers 22. Along the way, the metal wire 12 passes through a form74, made of a high temperature resistant material, e.g., one with a verylow coefficient of thermal expansion. The metal micro wire 12 issupported along its length in a through hole (which may have a taperedentrance) of the high temperature resistant form 74, oriented in alongitudinal plane of the metal wire. Examples of materials which may beused for form 74 include fused quartz, fused silica, and ceramic glass.

Near the end of the form 74 is nozzle area 18. An electrical heater 84,operated under the control of controller 30, is affixed to the end of apiezo translator 72 and abuts the exposed end of micro metal wire 12near the nozzle area 18, where the end of the metal micro wire has beenpositioned by piezo translator 20. The energy imparted by the electricalheater is used instead of a laser to melt the end of micro wire 12 nearthe nozzle area 18 and form a metal droplet. Although not shown in theillustration, the nozzle area 18 may be in close proximity to areceiving substrate on which the metal droplet is deposited. Jettingoverlapped metal droplets in this fashion in shapes defined bycross-sections of the object being manufactured results in the formationof the object. Piezo transducer 72 may be actuated, under the control ofcontroller 30, during formation of the droplet to assist in its ejectionfrom the nozzle area 18 and/or adjusted to control the amount of wire 12exposed to the laser so as to control the size of the droplet.

FIGS. 13A-13F illustrate the formation of a metal droplet in systemssimilar to that shown in FIG. 12A. The same principles of operationapply to systems such as that shown in FIG. 12B. Also, the operation ofthe piezo transduced 72 is applicable to the systems shown in FIGS.9-11, even though no heater element 84 need be used in thoseembodiments. In FIG. 13A, metal micro wire 12 has been positioned bypiezo translator 20 (not shown) so that the end of the metal wire iswithin the nozzle area 18, abutting the heating element 84 at positionp1. Heating element 84 is affixed at the end of piezo translator 72 sothat when piezo translator 72 is activated, the heating element will betranslated in a longitudinal direction with respect to metal wire 12,causing the end of metal wire 12 to deform, as described further below.At the time illustrated in FIG. 13A, piezo translator 72 has not beenactivated, but an electrical current has been applied to heating element84. As a result, the end of metal wire 12 is being heated, but it hasnot yet reached its melting point. In this example, the reaction area 78is filled with a high-pressure gas, preferably an inert gas such asArgon or Helium, introduced through gas inlet 80. The use of a gaswithin reaction area 78 helps to minimize or prevent oxidation of thatportion of metal wire 12 exposed within the reaction area 78, but isoptional. As will be discussed below, the presence of a gas underpressure within the reaction area can assist in jetting a metal dropletout of nozzle area 18 towards a receiving substrate.

FIG. 13B shows the system a few moments later than at the time depictedin FIG. 13A. As illustrated in the accompanying graphs, the electricalcurrent has been applied to the heating element 84 for some time, suchthat the metal wire 12 has now been heated throughout its length withinthe nozzle area 18. The piezo transducer 72 has not yet been activated,hence, the end of heating element 84 is still at position p1 and metalwire 12 has not yet been deformed.

FIG. 13C now shows the system a few moments later than at the timeillustrated in FIG. 13B. The magnitude of the electrical current appliedto heating element 84 has increased and the piezo transduced 72 has beenactivated. As a result, the end of metal wire 12 is heated to highertemperatures, allowing it to be deformed as shown when piezo transducer72 translates a distance laterally, causing the end of the heatingelement to now be at position p2. The elevated temperature of the metalwire causes it to become pliable such that it undergoes deformation whenthe heating element 84 at the end of piezo transducer 72 moves fromposition p1 to p2. Because of the presence of the high-pressure gaswithin the reaction area 78, the metal wire 12 is deformed towards thenozzle area 18, which is at lower (e.g., room) pressure. The movement ofthe heating element 84 causes it to come into contact with areas of wire12 larger than its end cross section, aiding in the heating process.

FIG. 13D shows the system a few moments later than at the timeillustrated in FIG. 13C. The piezo transducer 72 has completed itstranslation so that the portion of the metal wire 12 that has become hotand pliable has formed a droplet 32 that has been detached from theremainder of metal wire 12 and jetted, under the influence of thehigh-pressure gas and/or gravity, towards the receiving substrate (notshown). When the piezo translator reaches the extent of its lateralmovement, characterized by the heating element 84 now being at positionp3 at or near the end of the nozzle area 18, the electric current to thepiezo translator is turned off, causing the piezo translator to returnto its original position, as shown in FIG. 13E. Also, the electricalcurrent to heating element 84 is turned off. In some embodiments, thetiming of the electrical pulses to the heating element 84 and the piezotranslator 72 may be time-based, according to programs executed by timedby controller 30 (not shown here), and/or may be based on visualobservations of the condition of metal wire 12 and the formation ofdroplets 32 as provided by one or more cameras (not shown).

As illustrated in FIGS. 13E and 13F, when the piezo translator 72 andheating element 84 have returned to their original positions, the metalmicro wire 12 is translated by piezo translator 20 (not shown here) sothat the end of the wire is positioned abutting the heating element atp1. From this state of the system, the above-described process may berepeated to for a new metal droplet. Prior to doing so, the receivingsubstrate may be repositioned with respect to the nozzle area 18 so thatthe next droplet will be jetted to a desired position consistent withthat required for formation of the object under construction.

Referring now to FIG. 14, a further example of a metal micro wire 12disposed within an arrangement configured to cause jetting of metaldroplets is illustrated. In this example, details of the apparatusrelating to the feeding of the wire into the area at which laserirradiation is provided are not shown, but may be similar to any ofthose in the embodiments described above. Further, in this illustrationthe supporting arrangement 86 for micro wire 12 is shown as including atransparent (at the wavelength of the laser beam) portion 88 a and anontransparent portion 88 b. In other embodiments, however, atransparent support 24, as described above, may be used. Where a two (ormore) piece supporting structure 86 is used, the portions of thesupporting structure may be held together using pins 90 (e.g., which maybe threaded, or partially so, to allow for secure joining of the pieces.

As shown at right (which is a bottom view of the arrangement), thethrough hole 92 in this embodiment has a triangular shape. In oneembodiment, this shape may be provided by notching a “v”-shaped channelalong an edge of the transparent portion 88 b of the support structure86. When the two portions of the support structure are then combined,the smooth surface of the non-transparent portion 88 b will provide oneside to the triangular-shaped through hole, with the remaining two sidesprovided by the walls of the v-shaped groove in the transparent portion.Using a triangular-shaped through hole allows for the use of oil orgrease to lubricate the meal micro wire as it passes into the supportingarrangement 86. This reduces friction and adhesion of the metal microwire to the walls of the supporting arrangement, allowing the metalmicro wire to pass more easily through the through hole than if no suchlubricant were used. The lubricant may be applied near the entrance ofthe through hole along the path transited by the metal micro wire usingan appropriate dispenser 96. The dispenser may operate under the controlof the controller (not shown in this view) to dispense very smallamounts of lubricant either as needed (e.g., which may be determinedbased on feedback from the piezo translator or other measurementinstrument), or on a predetermined schedule, or both.

In embodiments of the invention, various metal micro wires, consistingof either or both pure metals and alloys, may be used. For example,wires made of any of Al, Au, Ag, Cu, W, or Ti, and/or alloys thereof,may be used.

Thus, methods and apparatus for additive manufacturing, and, inparticular, to such methods and apparatus as employ pulsed lasers orother heating arrangements to create metal droplets from donor microwires, which droplets, when solidified in the aggregate, form 3Dstructures, have been described.

What is claimed is:
 1. A system for metal laser jetting, comprising: asupply of metal micro wire arranged so as to be fed towards a reactionarea having an associated nozzle area by a translator, the metal microwire being supported along its length in a through hole of a form, thenozzle area being located near an exit of the through hole; and a heaterpositioned to contact an end of the metal micro wire adjacent the nozzlearea, thereby causing an end portion of the metal micro wire near thenozzle area to be heated.
 2. The system for metal laser jetting of claim1, wherein the form is shaped to change an orientation of the metalmicro wire from a first plane to a second plane as the metal micro wireis fed towards the nozzle area.
 3. The system for metal laser jetting ofclaim 1, further comprising a second translator adjacent the nozzlearea, the heater being positioned so as to be displaceable towards theend of the metal micro wire by the second piezo translator.
 4. Thesystem for metal laser jetting of claim 1, wherein the reaction areaincludes a gas inlet.
 5. The system for metal laser jetting of claim 1,further comprising a receiving substrate positioned to receive a dropletof metal from the nozzle area.
 6. The system for metal laser jetting ofclaim 1, wherein the supply of metal micro wire is organized in a spoolwhich is carried on a reel.
 7. The system for metal laser jetting ofclaim 1, wherein the supply of metal micro wire is organized in multiplespools of metal micro wires, each associated with its own respectivetranslator and supporting form.
 8. The system for metal laser jetting ofclaim 1, wherein the supply of metal micro wire is organized in multiplespools of metal micro wires and a single form is shared by some or allof the spools of metal micro wires.
 9. The system for metal laserjetting of claim 1, further comprising a heater affixed to one or moresides of the form to preheat the metal micro wire.
 10. The system formetal laser jetting of claim 1, wherein the translator includes one ormore piezo ceramics arranged to move the micro wire in a defineddirection upon application of an electric current under the control ofthe controller.
 11. The system for metal laser jetting of claim 1,wherein the translator comprises one or more longitudinal piezoactuators, one or more piezoelectric shear actuators, or one or moretube actuators.
 12. The system for metal laser jetting of claim 1,wherein a second translator is adjacent the nozzle area.
 13. A method offorming a three-dimensional (3D) article by fusion of metal droplets informs defined by cross-sections of the article under construction, saidmethod comprising distributing successive layers of metal droplets overa receiving medium and previously deposited layers of metal droplets bydepositing the droplets while moving the receiving medium relative to anozzle area of a metal laser jetting system, in which system a supply ofmetal micro wire is fed towards the nozzle area at which an end portionof the metal micro wire is heated by a heater, thereby causing the endportion of the metal micro wire near the nozzle area to form thedroplets, said moving occurring between successive ones of the dropletsto form layers of metal on the receiving medium and, successively, onpreviously jetted layers.
 14. The method of claim 13, wherein as themetal micro wire is fed towards the nozzle area the metal micro wirepasses through a through hole in a form.
 15. The method of claim 14,wherein the reaction area is disposed within the form, such that aportion of the metal micro wire is exposed within the reaction area whenexiting the through hole, and prior to heating of the metal micro wirethe reaction area is filled with a gas introduced through a gas inlet.16. The method of claim 13, wherein the heater is operated under controlof a controller, and is affixed to an end of a piezo translator, whichpiezo translator is operated so as to cause the heater to abut anexposed end of the micro metal wire near the nozzle area, therebyheating the end of the metal micro wire near the nozzle area and forminga metal droplet.
 17. The method of claim 13, wherein as the metal microwire is fed towards the nozzle area the metal wire passes through athrough hole in a form articulated to change an orientation of the wirefrom a first plane to a second plane.